Why does it all matter?

Sentencing issues

Kaczynski's defense team would have liked to introduce evidence which supported
a "not guilty by reason of insanity" judgment. Success on those grounds
would have resulted in an acquittal of the defendant, and in his probably
committal to a government psychiatric institution. However, Kaczynski refused
to allow his attorneys to pursue this course.

The defense attorneys would not like to be allowed to argue the "diminished
capacity" defense. If this defense is successful, it might have one of
two effects:

First, the jury might decide that Kaczynski lacked the necessary presence
of mind for murder or another crime which required premeditation or wilfullness,
and acquit him of the more serious charges; or

Second, during the sentencing phase, the judge is permitted to depart
downward from the federal sentencing guidelines for defendants with diminished
capacity.

Evidentiary issues

The prosecution sees diminished capacity essentially as a sentencing matter.
They argue that allowing evidence of Kaczynski's paranoid schizophrenia
would unduly bias the jury in his favor and would distract jury members
from the issue at hand: whetehr Kaczynski committed the acts of which he
is accused. They want the judge to refuse to permit such evidence to be
presented to the jury.

Furthermore, the prosecutors are upset that Kaczynski will not allow
government experts to interview him. In the interest of fairness, they
argue, the defense must not be allowed to present evidence which results
from its own witnesses' interviews with Kaczynski.